1. Field of the Invention
The invention relates to a secondary air supply apparatus and a control method for the same. More specifically, the invention relates to a secondary air supply apparatus or a method for the same, which can detect failure in the secondary air supply apparatus.
2. Description of the Related Art
A secondary air supply apparatus is known, which supplies an exhaust manifold of an engine with secondary air delivered under pressure from an air pump so that CO and HC in exhaust gas are burned and changed to CO2 and H2O due to chemical reaction.
Japanese Patent Application Publication No. JP 2003-83048 discloses a secondary air supply apparatus in which it can be determined whether an abnormality has occurred in a component of the secondary air supply apparatus. The secondary air supply apparatus disclosed in the Japanese Patent Application Publication No. JP 2003-83048 includes a secondary air supply passage for supplying secondary air to a portion upstream of an exhaust gas control device in an exhaust system of an internal combustion engine; an opening/closing portion which opens/closes the secondary air supply passage; a check valve which is provided downstream of the opening/closing portion; a pressure sensor which is provided in the secondary air supply passage; and an abnormality detecting portion which detects an abnormality in the component based on a pressure value detected by the pressure sensor and a pressure change value. When the opening/closing portion is controlled so as to open and close the secondary air supply passage, the abnormality detecting portion drives an air pump, and detects a discharge pressure of the air pump, thereby detecting clogging of the secondary air supply passage.
In the secondary air supply apparatus disclosed in the Japanese Patent Application Publication No. JP 2003-83048, since the pressure value and the pressure change value are obtained using the pressure sensor, a failure mode of each component can be determined in detail based on combination of the pressure value and the pressure change value. Also, since the air pump is driven and it is determined whether the discharge pressure of the air pump decreases when the opening/closing portion is controlled to close the secondary air supply passage, it is possible to determine whether an abnormality has occurred in the air pump, and to determine whether the secondary air supply passage has been clogged, at the same time.
However, in the secondary air supply apparatus disclosed in the Japanese Patent Application Publication No. JP 2003-83048, it may not be possible to accurately determine whether an abnormality has occurred. The secondary air supply apparatus is made on the precondition that the opening/closing portion which opens/closes the secondary air supply passage; and the check valve which is provided downstream of the opening/closing portion are provided. However, no consideration is given to a secondary air supply apparatus having a configuration other than this configuration. Accordingly, in a secondary air supply apparatus having a configuration other than this configuration, it may not be possible to accurately determine whether an abnormality has occurred. Also, in the secondary air supply apparatus disclosed in the aforementioned publication, the air pump is driven and the discharge pressure of the air pump is detected, whereby it is determined whether the secondary air supply passage has been clogged, at the same time. However, it may be inappropriate to drive the air pump in some cases.